2 King Edward or Maris Piper potatoes, peeled and sliced with a mandolin
1 garlic clove, finely chopped
1 tbsp chopped fresh flat leaf parsley
1 rosemary sprig
1 tbsp Dijon mustard
100ml/3½fl oz dark veal glacé or beef stock
salt and freshly ground black pepper
1–2 tbsp olive oil
25g/1oz unsalted butter
2 rib-eye steak (200g/7oz each), at room temperature